Four leg magnetic core



United States Patent FOUR LEG MAGNETIC CORE Wallace M. Johnson, Pittsfield, Mass., assignor to General Electric Company, a corporation oi New York Application November 20, 1953, Serial No. 393,422

6 Claims. (Cl. 336-212) This invention relates to a four-leg magnetic core providing maximum utilization of core materials; more particularly, the invention relates to a single-phase transformer utilizing a four-leg magnetic core.

Magnetic cores having four legs have a lower silhouette than magnetic cores of the same capacity having two legs. Maximum railway clearances limit the height of large power transformers and the lower height required for the same window height in a four-leg transformer makes this design very attractive for certain installations. In the past, four-leg construction has been accomplished by mounting three rectangular cores of equal cross-sectional area in appropriate spaced relation. With this conventional iour leg construction, the magnetic flux in the outer legs is the same as the magnetic flux in each half of the inner legs. This does not provide the maximum utilization of core materials.

it is an object of the present invention to provide a four-leg magnetic core in which there is improved utilization of the core materials.

It is another object of this invention to provide a fourleg magnetic core with a very effective cooling duct arrangement.

Other objects will be apparent from the following specification considered in connection with the accompanying drawings in which Fig. 1 is an elevational view of a transformer constructed in accordance with this invention and Fig. 2 is a graph illustrating the advantages accruing from construction in accordance with this invention.

Briefly stated, in accordance with one of its aspects, the invention consists of a magnetic core assembly comprising a central core of magnetic material having a rectangular profile defining a central rectangular window, and a spaced magnetic side core on each side of the central core, the side cores having the same window height as the central core window and having a cross-sectional area of less than two-thirds of the cross-sectional area of the central core.

Referring to Fig. 1, the transformer of this invention comprises an inner magnetic core 10 and an outer magnetic core 11 of rectangular profile, the cores 10 and 11 being in spaced nesting relationship to each other to provide a cross cooling or ventilating passageway or duct 13. The cores 10 and 11 are preferably composed of a magnetically on'ented silicon steel laminations. At each side or the outer core 11 is a side core 14 or 15 spaced a short distance from the core 11 in order to provide a cooling passageway 12. The cores 14 and 15 are preferably composed of the same materials as the cores .10 and 11. However, the cross-sectional area of each of the cores 14 and 15 is less than two-thirds of the combined crossseetional areas of the cores 10 and 11, the cross-sectional area of the side cores preferably being between one-ninth and two-thirds of the crosssectional area of the central cores. A preferred proportion within this range is to have the side cores with about one-third the cross-sectional area of the central cores. While there is a central core 2,780,786 Patented Feb. 5, 1957 consisting of an inner and outer portion, it is obvious that the transformer would function with just a single integral central core. Irrespective of the number of central core parts the proportion of cross-sectional area of side core to central core or cores is maintained.

The window height is the same for the central core 10 and the side cores 14 and 15. However, the side cores i4 and 15 may have a lesser width since a pair of inductive windings 16 and 17 which may both be on one leg or divided and a portion of each on each leg, can be accommodated with a window of lesser width in the side cores than in the central core. Their thickness may also be less than the thickness of the central core portions.

The advantage obtained from a four-leg core is that the height of the yoke is reduced thereby permitting a higher window with the same overall core height. The core illustrated differs from previous four-leg cores not only in the duct arrangement but in having three-fifths of the magnetic circuit closed through the top and bottom yoltes and the remaining part of the magnetic circuit through the outside legs in the case of a cross-sectional area ratio of two-thirds: one for the side core center core. in the case of smaller side cores still more of the magnetic circuit is closed through the top and bottom yokes. This provides better utilization of the core materials than the conventional four-leg core since the cross-section of the longer magnetic path is proportionally less than in the conventional four-leg core. This core also provides a smaller unbalance between parallel magnetic circuits than the conventional four-leg type of core.

The graph of Fig. 2 illustrates the changes in core Weight for different ratios of side core cross-sectional areas S to center core cross-sectional area C for three ditferent window heights. An S/C ratio of 0 gives the weight of a conventional two-leg core and a ratio of 1.0 gives the weight of a conventional four-leg core. It may be seen that as the permissible window height decreases the advantages of the construction of this invention are considerably increased.

While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. Therefore, I aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A four-leg magnetic core assembly comprising a central core of magnetic material having a pair of oppositely disposed winding legs and a rectangular profile defining a central rectangular window, and a rectangular magnetic side core adjacent each of said winding legs, said side cores having the same window height as said central core window and having a cross-sectional area less than two-thirds the cross-sectional area of the central core.

2. A four-leg magnetic core assembly comprising a central core of magnetic material having a pair of oppositely disposed winding legs and a rectangular profile defining a central rectangular window, and a rectangular magnetic side core adjacent each of said winding legs, said side cores having the same window height as said central core window and having a cross-sectional area between one-ninth and two-thirds of the cross-sectional area of the central core.

3. A four-leg magnetic core assembly comprising a central core of magnetic material having a pair of oppositely disposed winding legs and a rectangular profile defining a central rectangular window, and a rectangular magnetic side core adjacent each of said winding legs, said side cores having the same window height as said central core window and having a cross-sectional area of about one-third the cross-sectional area of the central core.

4. A four-leg magnetic core assembly comprising a pair of spaced nested central coaxial cores of magnetic material having a rectangular profile and a pair of oppositely disposed winding legs, the inner central core defining a central rectangular window, and a magnetic side core of rectangular profile adjacent each of said winding legs and spaced therefrom, said side cores defining windows having the same height as said inner central core window and having a cross-sectional area less than twothirds of the combined crosssectional areas of said central cores.

5. A four-leg magnetic core assembly comprising an inner and outer central magnetic core of rectangular profile and having a pair of oppositely disposed winding legs. said cores being in spaced nesting coaxial relationship to each other to provide a cross cooling duct, the inner of said cores defining a rectangular window, and a magnetic side core of rectangular profile adjacent each of said winding legs and spaced therefrom, said side cores defining windows having the same height as said inner central core window and having a cross-sectional area between one-ninth and two-thirds of the sum of the cross-sectional areas of the inner and outer central cores.

Lil)

6. A single-phase transformer comprising an inner and outer central magnetic core of rectangular profile and having a pair of oppositely disposed winding legs, said cores being in spaced nesting coaxial relationship to each other to provide a cross cooling duct, the inner of said cores defining a rectangular window, a rectangular magnetic side core adjacent each of said winding legs and spaced therefrom, said side cores defining windows having the same height as said inner central core window and having a crosssectional area between one-ninth and twothirds ol the sum of the cross-sectional areas of the inner and outer central cores, said cores forming two groups with three core legs in each group, a primary winding on at least one of said groups of legs, and a secondary winding on at least the other of said groups of legs.

References Cited in the file of this patent UNITED STATES PATENTS 755,766 Hall Mar. 29, 1904 765,483 Cole June 24, 1930 l,89l,l78 Porter Dec. 13, 1932 FOREIGN PATENTS 309,926 Great Britain Jan. 30, 1930 

